1. Field of the Invention
This invention relates to a process for the production of fatty ketones by pyrolysis of fatty acid magnesium salts.
2. Statement of Related Art
Long-chain symmetric and asymmetric ketones based on fatty acids, so-called "fatty ketones" are used either directly or after sulfonation or quaternization as additives for fabric softeners, hair shampoos, corrosion inhibitors or flotation aids (Chem. Ing.-Tech. 62, 416 and 512 (1990).
The production of fatty ketones by pyrolysis of fatty acid salts in the presence of catalytic quantities of calcium, iron or manganese salts has been known since 1855 and is covered by extensive literature (Houben-Weyl, Methoden der Organischen Chemie, Thieme-Verlag, Stuttgart, Vol. 7/2a, pages 622 et seq.).
Recently, magnesium oxide has been successfully used as the catalyst. Thus, a laboratory process for the production of stearone, in which 1 mole of stearic acid and 0.5 mole of magnesium oxide are reacted at 340.degree. C., is described, for example, in Org. Synth., Vol. 33, pages 854 et seq. For working up, the crude product has first to be washed with sulfuric acid, water and sodium hydrogen carbonate solution, the pure stearone only being obtained after two crystallizations. In addition, it is recommended that foam formed during the reaction be either mechanically destroyed or controlled by antifoam agents. In overall terms, a process such as this is unsuitable for industrial application on account of the high outlay on equipment for working up.
A process for the production of fatty ketones by pyrolysis of magnesium salts of fatty acids is also known from J. Soc. Chem. Ind. 66, 402 (1947). To solve the foam problems, it is proposed in this reference initially to introduce the fatty acid in far less than the equivalent quantity relative to the magnesium oxide, to heat the reaction mixture and then continuously to introduce the remaining fatty acid. Although foam problems can be minimized in this way, they cannot be eliminated altogether so that part of the fatty acid is still discharged and is thus lost in the absence of additional measures. Another disadvantage of the process is that the magnesium salt has to be separated by filtration, sedimentation or treatment with mineral acids after the reaction and, accordingly, cannot be quantitatively removed from the products.
Accordingly, the problem addressed by the present invention was to provide a new process for the production of fatty ketones which would not have any of the disadvantages described above.